The present invention relates to a suspending medium for use in immunologic reactions. More particularly, the invention relates to a suspending medium for immunohematologic reactions and to a method for potentiating agglutination reactions.
Immunohematologic agglutination reactions have conventionally been conducted in media comprised of physiological saline (ca. 0.15M NaCl) or albumin solutions. Thus, in antibody screening, antibody identification, crossmatches, direct or indirect antiglobulin testing, blood grouping, and the like, cells are conventionally washed and suspended in physiological saline for reaction with test serums. The use of physiological saline in such reactions suffers from certain disadvantages. Notably, lengthy incubation times are often required to observe agglutination reactions. In certain situations, such as crossmatching for emergency transfusions, it is important to obtain reaction results as quickly as possible. Another disadvantage of physiological saline is that cells tend to be sticky and, thus, adhere to glass surfaces, making evaluation of reaction results difficult.
Physiological saline has been modified to overcome some of these disadvantages. Esposito, V. M. and Weinstein, S. B., U.S. Pat. No. 3,970,427, describe a suspending solution containing physiological saline and a small amount of gelatin. The addition of gelatin was found to reduce or eliminate the problem of sticking between erythrocytes and glass surfaces, and to reduce hemolysis. Another procedure in widespread use involves the addition of an albumin solution, e.g. 22% or 30% bovine albumin, to a suspension of cells in physiological saline. The albumin is thought to enhance the agglutination reaction by reducing the electrostatic charge on the cell surfaces. Technical Manual of the American Association of Blood Banks, Wm. V. Miller, Ed., American Association of Blood Banks, Washington, D.C., 1977, p. 167.
For many years, low ionic strength solutions, i.e. solutions having ionic strengths lower than that of physiological saline, have been known to enhance agglutination in many immunologic tests. However, the procedures employing such solutions produced an unacceptable incidence of false (non-antibody) positive reactions and stymied their general acceptance. Low, B. and Messeter, L., Vox. Sang. 26, 53-61 (1974) reported a low ionic strength solution which included sodium glycinate. That solution produced few false positive reactions, and when compared to standard procedures employing physiological saline or bovine albumin, a reduction in required incubation times with specific antibody-containing serums was realized. The solution also increased the antibody uptake and the strengths of agglutination reactions with certain antibodies. Subsequent work indicates that procedures employing low ionic strength suspending media are at least as sensitive, and in most cases are more sensitive, than routine procedures employing physiological saline or albumin for the detection of IgG and IgM antibodies.